The invention relates to an infrared quantum structure imaging device or imaging device working at ambient temperature.
The field of the invention relates to the detection of infrared transmissions. Chiefly, two detection mechanisms are used at the present time:
heat sensors which use the variations of a physical parameter (resistivity, capacity, etc.) with the heating due to the absorption of the infrared wave; PA1 quantum sensors which use the transition between two series of quantum levels separated by a forbidden energy gap.
The quantum sensors are particularly valuable because their ultimate performance in terms of detectivity is far greater than that of heat sensors. Thus the values of detectivity of 3.times.10.sup.11 cm/Hz .sup.1/2 W are obtained in the II band (between 3 and 5 .mu.m) with sensors based on semiconductors such as HgCdTe or PbSnTe. These results are more than 20 times higher than those obtained with heat sensors. However, unlike heat sensors, these quantum sensors suffer from the fact that they have to be cooled to be able to work. Typically, they work at temperatures in the range of 80 K.
The French patent application No. 96 15738 describes a quantum sensor working at ambient temperature or close to ambient temperature (250-300 K). This sensor has resonant coupling arrays that increase the values of detectivity of quantum sensors. FIG. 2 shows the noise equivalent temperature detectable values (NETD) that can be obtained in an optimized structure based on a heterostructure of InAs.sub.0.95 Sb.sub.0.15 (0.1 .mu.m)/GaSb with a surface area of 40.times.40 .mu.m.sup.2, for a 20 Hz passband and different non-radiative lifetimes in the material.
It can be seen that the performance characteristics of the sensor depend considerably on the temperature. Thus, for a lifetime of 30 ns of the photocarriers, the NETD goes from 40 mK to 5 mK when the temperature goes from 300 to 150 K.
A sensor of this kind does not require any cooling in order to function. However, it may be necessary to improve the performance characteristics and especially to reduce the NETD.